As far as I can ascertain Hugh and Mary had the following children:-

Joseph baptised 13/1/1793
Jane 1/2/1795
Elizabeth 23/7/1797
Ann 9/3/1800
Benjamin 3/10/1802 (my Gtx3 Grandfather who married Christian Alexander 1826
Hugh 3/2/1805
Mary 19/8/1807 Bap at St Nicholas Liverpool
John 11/10/1810 St Johns Old Haymarket
Christiana 30/8/1812 " " " Lpool

Frances interesting you mentioned Benj could have been known as John? I have him on later Census records and always as Benjamin -is there a record of a John born around same time? They had a son John born in 1810 but they were in Liverpool by then.